Semiconductor device

ABSTRACT

A semiconductor device includes a semiconductor substrate having opposed main and back surfaces; first and second electrodes in a device region of the substrate, and spaced apart from each other; a metal film on the main surface and joined to the second electrode; an air gap between part of the main surface and the metal film, enveloping the first electrode, and having an opening; a cured resin closing the opening; a liquid repellent film increasing contact angle of the resin, relative to contact angles on the substrate and the metal film; a first metal film joined to the metal film, covering the metal film and the cured resin, and joined to an outer peripheral region of the substrate, at a periphery of the device region; and a second metal film on the back surface and connected to the first electrode through a via hole penetrating the substrate.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a semiconductor device and method formanufacturing the same using a non-hermetic package such as a moldpackage, and in particular to a semiconductor device and method formanufacturing the same which can prevent deterioration of radiofrequencycharacteristics and improve the moisture resistance.

2. Background Art

Schemes to generalize radiofrequency semiconductor devices such as fieldeffect transistors using a chemical compound semiconductor such as GaAsor GaN are rapidly progressing and there is a strong demand for a costreduction effect. As a means for meeting this demand, using low-pricedmold packages instead of completely hermetic metal packages heretoforeused has become practical. In a case where a non-hermetic package suchas a mold package is used for a semiconductor device, however, it isnecessary to improve the moisture resistance of the semiconductor devicein order to prevent deterioration in various respects due to causesrelating to water.

Conventionally, electrodes provided on a main surface of a semiconductorsubstrate are covered with thick insulating film such as SiN film formedby plasma CVD or the like, thereby preventing permeation of water andsecuring the moisture resistance.

The existence of the thick insulating film having a high dielectricconstant between the semiconductor substrate and the electrodes,however, entails a problem that the capacitive components are increasedand the radiofrequency characteristics are deteriorated. Insulating filmformed by plasma CVD or the like easily absorbs moisture, depending onthe film forming condition. If the film thickness is increased, theinsulating film can be separated by a change in stress when it absorbs asmall amount of water. In such case, the coverage and film quality at astepped portion of a transistor are deteriorated to allow water toeasily pass through or to be absorbed in the film. It is, therefore,difficult to effectively prevent permeation of water to the transistor.

A semiconductor device has been proposed that has a construction forpreventing deterioration of radiofrequency characteristics in which anair gap is formed between a main surface of a semiconductor substrateand an air gap forming film; the air gap envelops gate electrodes anddrain electrodes; and an opening of the air gap is closed with a resin(see, for example, Japanese Patent Laid-Open No. 2009-184067,particularly FIGS. 30 and 31).

In Japanese Patent Laid-Open No. 2009-184067, the method of connectingthe electrodes in the air gap to electrode pads outside the air gap isnot described in detail. In a case where the electrodes and theelectrode pads are connected to each other by metal wirings, an end ofeach metal wiring is connected to the electrode and the other end of themetal wiring is led out of the resin to be connected to the electrodepad. However, a gap can occur easily at the interface between the metalwiring and the resin when the resin is thermally cured in themanufacturing process. As a result, the moisture resistance isdeteriorated.

SUMMARY OF THE INVENTION

In view of the above-described problems, an object of the presentinvention is to provide a semiconductor device and method formanufacturing the same which can prevent deterioration of radiofrequencycharacteristics and improve the moisture resistance.

According to the present invention, a semiconductor device includes: asemiconductor substrate having a main surface; an electrode in a deviceregion on the main surface; a metal wiring on the main surface andhaving a first end connected to the electrode; an electrode pad outsidethe device region on the main surface and distanced from the metalwiring; an air gap forming film on the main surface; an air gap betweena part of the main surface and the air gap forming film, enveloping afirst end of the metal wiring and the electrode, and having a firstopening; a resin closing the first opening and covering a second end ofthe metal wiring without covering the electrode pad; a liquid repellentfilm on an internal surface facing the air gap and having such aphysical property as to increase a contact angle of the resin in aliquid state relative to those on the semiconductor substrate and theair gap forming film; and a metal film connecting the metal wiring tothe electrode pad through a second opening provided in the cured resin,wherein the second end of the metal wiring is not jutted out of theresin.

The present invention makes it possible to prevent deterioration ofradiofrequency characteristics and improve the moisture resistance.

Other and further objects, features and advantages of the invention willappear more fully from the following description.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a top view of a semiconductor device according to a firstembodiment of the present invention.

FIG. 2 is a sectional view taken along line I-I in FIG. 1.

FIG. 3 is a sectional view taken along line II-II in FIG. 1.

FIG. 4 is a top view at the height corresponding to line II-II in FIG.2.

FIGS. 5 to 13 are sectional views showing a process of manufacturing thesemiconductor device according to the first embodiment of the presentinvention.

FIG. 14 is a sectional view of a semiconductor device according to thecomparative example.

FIG. 15 is a sectional view showing a first modified example of asemiconductor device according to the first embodiment of the presentinvention.

FIG. 16 is a sectional view showing a second modified example of asemiconductor device according to the first embodiment of the presentinvention.

FIG. 17 is a sectional view of a semiconductor device according to asecond embodiment of the present invention.

FIG. 18 is a sectional view of a semiconductor device according to athird embodiment of the present invention.

FIG. 19 is a top view of a semiconductor device according to a fourthembodiment of the present invention.

FIG. 20 is a bottom view of the semiconductor device according to thefourth embodiment of the present invention.

FIG. 21 is a sectional view taken along line I-I in FIG. 19.

FIG. 22 is a top view at the height corresponding to line II-II in FIG.21.

FIG. 23 is a sectional view of a semiconductor device according to afifth embodiment of the present invention.

FIG. 24 is a top view of a semiconductor device according to a sixthembodiment of the present invention.

FIG. 25 is a sectional view taken along line I-I in FIG. 24.

FIG. 26 is a top view at the height corresponding to line II-II in FIG.25.

FIG. 27 is a top view of a semiconductor device according to a seventhembodiment of the present invention.

FIG. 28 is a bottom view of the semiconductor device according to theseventh embodiment of the present invention.

FIG. 29 is a sectional view taken along line I-I in FIG. 27.

FIG. 30 is a top view at the height corresponding to line II-II in FIG.29.

FIG. 31 is a top view of internal portions of a semiconductor deviceaccording to an eighth embodiment of the present invention.

FIG. 32 is a bottom view showing the semiconductor device according tothe eighth embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

A semiconductor device and method for manufacturing the same accordingto the embodiments of the present invention will be described withreference to the drawings. The same components will be denoted by thesame symbols, and the repeated description thereof may be omitted.

First Embodiment

FIG. 1 is a top view of a semiconductor device according to a firstembodiment of the present invention. FIG. 2 is a sectional view takenalong line I-I in FIG. 1. FIG. 3 is a sectional view taken along lineII-II in FIG. 1. FIG. 4 is a top view at the height corresponding toline II-II in FIG. 2.

A drain electrode 2 and a source electrode 3 are provided in a deviceregion on a main surface of a semiconductor substrate 1 while beingspaced apart from each other. A gate electrode 4 is provided between thedrain electrode 2 and the source electrode 3. Each of the drainelectrode 2 and the source electrode 3 is an ohmic metal layer. The gateelectrode 4 is a Schottky electrode. A drain wiring 5 having its one endconnected to the drain electrode 2 is provided on the main surface. Asource wiring 6 is also provided on the source electrode 3. Theseelements constitute a transistor. The surfaces of these elements areprotected by a SiN film 7. In a place where the SiN film 7 is notnecessary, e.g., a place above the source wiring 6 on the sourceelectrode 3, a contact hole is formed in the SiN film 7.

A plated feed layer 8 and an Au plated layer 9 are provided on the mainsurface and connected to the source electrode 3 through the sourcewiring 6. An air gap 10 is formed between the plated feed layer 8/Auplated layer 9 and a portion of the main surface. The air gap 10envelopes one end of the drain wiring 5, the gate electrode 4 and thedrain electrode 2 and has an opening 11. A drain electrode pad 12 and agate electrode pad 13 are provided outside the device region on the mainsurface. The drain electrode pad 12 and the drain wiring 5 are distancedfrom each other.

Cured polyimide film 14 closes opening 11 and covers the other end ofthe drain wiring 5 without covering the drain electrode pad 12 and thegate electrode pad 13. The other end of the drain wiring 5 is not juttedout of the polyimide film 14. A liquid repellent film 15 is provided onthe internal surface facing the air gap 10. The liquid repellent film 15has such a physical property as to increase the contact angle of thepolyimide film 14 in a liquid state relative to those on thesemiconductor substrate 1, the plated feed layer 8 and the Au platedlayer 9.

Through an opening 16 provided in the cured (imidized) polyimide film14, the other end of the drain wiring 5 and the drain electrode pad 12are connected to each other by a plated feed layer 17 and an Au platedlayer 18. A gate wiring (not shown) connected to the gate electrode 4and the gate electrode pad 13 are also connected in the same way.

A method of manufacturing the semiconductor device according to thepresent embodiment will next be described. FIGS. 5 to 13 are sectionalviews showing a process of manufacturing the semiconductor deviceaccording to the first embodiment of the present invention.

First, as shown in FIG. 5, the gate electrodes 4, drain electrodes 2 andsource electrodes 3 are formed in a device region on the main surface ofthe semiconductor substrate 1. The drain wirings 5 having their one endsconnected to the drain electrode 2 are formed on the main surface. TheSiN film 7 is formed as insulating protective film on the surfaces ofthese elements by plasma CVD, and contact holes are formed in the SiNfilm 7.

Next, as shown in FIG. 6, a photoresist film 19 is applied to the entiresurface and openings are formed in the photoresist film 19 above thesource wirings 6 on the source electrodes 3 by a transfer process.

Next, as shown in FIG. 7, the plated feed layer 8 formed of Ti/Au isformed on the entire surface, for example, by sputtering.

Next, as shown in FIG. 8, a photoresist film 20 is applied to the entiresurface and an opening is formed in the photoresist film 20 by atransfer process. Thereafter, the Au plated layer 9 is formed byelectrolytic plating on the plated feed layer 8 in the opening in thephotoresist film 20. At this time, the drain electrode pad 12 and thegate electrode pad 13 are formed outside the device region on the mainsurface.

Next, as shown in FIGS. 9 and 10, the photoresist film 20 is removed andthe plated feed layer 8 in the region where the photoresist film 20 hasbeen removed is removed, for example, by ion milling. The photoresistfilm 19 is thereafter removed. The air gaps 10 are thereby formedbetween the plated feed layer 8/Au plated layer 9 and portions of themain surface.

Next, as shown in FIGS. 11 and 12, the liquid repellent film 15 isformed on the entire surface by an isotropic film forming method. Theisotropic film forming method is a film forming method of depositing amaterial to be formed as a film so that the deposited material isgenerally uniform in thickness no matter what the orientation andposition of the surface on which the film is formed. Therefore theliquid repellent film 15 having a sufficient thickness can be formedeven on the internal surfaces facing the air gaps 10. Thereafter, theunnecessary liquid repellent film 15 formed on portions other than theinternal surfaces facing the air gaps 10 is removed, for example, byanisotropic etching using a RIE apparatus.

Next, as shown in FIG. 13, a photosensitive polyimide film 14 in liquidform is applied to the entire surface, for example, by using a spraycoater or a spin coater. With the polyimide film 14, the openings 11 ofthe air gaps 10 are closed and the other ends of the drain wirings 5 arecovered. The polyimide film 14 is thereafter cured. At this time, theair gaps 10 are maintained by the effect of the liquid repellent film 15without being filled with the polyimide film 14. Next, the opening 16 isformed in the cured polyimide film 14 on the other ends of the drainwirings 5 by a transfer process.

Next, as shown in FIGS. 1 and 2, the plated feed layer 17 and the Auplated layer 18 are formed and patterned by the same method as that offorming the plated feed layer 8 and the Au plated layer 9. The platedfeed layer 17 and the Au plated layer 18 that connect the other ends ofthe drain wirings 5 and the drain electrode pad 12 to each other throughthe opening 16 are thereby formed.

The effects of the present embodiment will be described. In the presentembodiment, the air gap 10 is formed between the plated feed layer 8/Auplated layer 9 and a portion of the main surface. The air gap 10envelops one end of the drain wiring 5, the drain electrode 2 and thegate electrode 4 in the device region. Thus, no insulating film of ahigh dielectric constant exists between the semiconductor substrate 1and the gate electrode 4 and between the semiconductor substrate 1 andthe drain electrode 2. Prevention of deterioration of radiofrequencycharacteristics is thus enabled.

Another effect of the present embodiment will be described throughcomparison between the present embodiment and a comparative example.FIG. 14 is a sectional view of a semiconductor device according to thecomparative example. In the comparative example, the other end of thedrain wiring 5 is jutted out of the polyimide film 14 for connectionbetween the other end of the drain wiring 5 and the drain electrode pad12. Therefore, when the polyimide film 14 is heat-cured in themanufacturing process, a gap occurs at the interface between the drainwiring 5 and the polyimide film 14. This gap can be a path through whichwater can permeate into the air gap 10, resulting in deterioration ofthe moisture resistance.

On the other hand, in the present embodiment, the other end of the drainwiring 5 and the drain electrode pad 12 are connected to each other bythe plated feed layer 17 and the Au plated layer 18 through the opening16 provided in the cured polyimide film 14. This construction enablesavoiding jutting the other end of the drain wiring 5 out of thepolyimide film 14 and, hence, reducing the occurrence of a gap that canbe a path through which water can permeate into the air gap 10, thusimproving the moisture resistance.

FIG. 15 is a sectional view showing a first modified example of asemiconductor device according to the first embodiment of the presentinvention. The plated feed layer 17 and the Au plated layer 18completely cover a portion right above the opening 11. The moistureresistance can be further improved in this way.

FIG. 16 is a sectional view showing a second modified example of asemiconductor device according to the first embodiment of the presentinvention. While the plated feed layer 17 and the Au plated layer 18 areprovided as air bridge metal wiring in the above-described embodiment,the plated feed layer 17 and the Au plated layer 18 may alternatively beprovided as wiring different from air bridge metal wiring, as shown inFIG. 16. Deposited metal wiring may be substituted for the plated feedlayer 17 and the Au plated layer 18 if there is no step-cut problem,depending on the shape of the polyimide film 14.

Insulating protective film such as SiN film may be formed on thepolyimide film 14. The plated feed layer 17 and the Au plated layer 18are then formed on the polyimide film 14, with the insulating protectivefilm interposed therebetween. The adhesion between these layers and thepolyimide film 14 is thereby improved. The moisture resistance can befurther improved in this way.

Second Embodiment

FIG. 17 is a sectional view of a semiconductor device according to asecond embodiment of the present invention. In the present embodiment,the drain wiring 5 and the drain electrode pad 12 are connected to eachother by an epitaxial resistive layer 21 provided in the semiconductorsubstrate 1. However, the epitaxial resistive layer 21 is notexclusively used. A semiconductor layer doped with an impurity, such asa doped resistive layer, may suffice.

The periphery of the polyimide film 14 meets the epitaxial resistivelayer 21 right above the same. An ohmic metal 22 is provided to makeohmic contact between the epitaxial resistive layer 21 and the drainwiring 5. The connection (not shown) between the gate wiring connectedto the gate electrode 4 and the gate electrode pad 13 is also made inthe same way.

In the present embodiment, the drain wiring 5 and the drain electrodepad 12 are connected to each other by the epitaxial resistive layer 21without jutting the other end of the drain wiring 5 out of the polyimidefilm 14. This construction enables reducing the occurrence of a gap thatcan be a path through which water can permeate into the air gap 10, thusimproving the moisture resistance. Also, since the air gap 10 is formedin the same way as that in the first embodiment, prevention ofdeterioration of radiofrequency characteristics is also enabled.

Third Embodiment

FIG. 18 is a sectional view of a semiconductor device according to athird embodiment of the present invention. In the present embodiment,the drain wiring 5 and the drain electrode pad 12 are connected to eachother by a metal layer 23 embedded in the semiconductor substrate 1. Theconnection (not shown) between the gate wiring connected to the gateelectrode 4 and the gate electrode pad 13 is also made in the same way.The other components are the same as those in the second embodiment. Thesame effects as those of the second embodiment can also be obtained.

Fourth Embodiment

FIG. 19 is a top view of a semiconductor device according to a fourthembodiment of the present invention. FIG. 20 is a bottom view of thesemiconductor device according to the fourth embodiment of the presentinvention. FIG. 21 is a sectional view taken along line I-I in FIG. 19.FIG. 22 is a top view at the height corresponding to line II-II in FIG.21. Description will be made only of points of difference from the firstembodiment.

The other end of the drain wiring 5 is jutted out of the polyimide film14 to be connected to the drain electrode pad 12. The connection (notshown) between the gate wiring connected to the gate electrode 4 and thegate electrode pad 13 is also made in the same way. These components arecovered with a photosensitive polyimide film 24.

In the polyimide films 14 and 24, an opening is formed above the platedfeed layer 8 and the Au plated layer 9. Through this opening, a platedfeed layer 25 and an Au plated layer 26 are joined to the Au platedlayer 9. The plated feed layer 25 and the Au plated layer 26 completelycover the plated feed layer 8, the Au plated layer 9 and the polyimidefilm 14 in the device region and are joined to the semiconductorsubstrate 1 in an outer peripheral region at the periphery of the deviceregion.

Au plated layers 27 and 28 are provided on the back surface of thesemiconductor substrate 1. The Au plated layer 27 is connected to thedrain electrode 2 through a via hole 29 penetrating the semiconductorsubstrate 1 and the drain wiring 5. Also, the Au plated layer 28 isconnected to the gate electrode 4 through elements including a via hole30.

A method of forming the via holes 29 and 30 and the Au plated layers 27and 28 will be described. First, after forming the plated feed layer 25and the Au plated layer 26, the thickness of the semiconductor substrate1 is reduced from the back surface side. Next, the back surface of thesemiconductor substrate 1 is dry-etched by using a photoresist as a maskto expose the plated feed layer 25, thereby forming the via holes 29 and30. An Au plated layer is then formed on the entire surface and atransfer process is performed. The Au plated layer in the unnecessaryregion is removed after the transfer process, for example, by using anAu etching solution (an aqueous solution mixture of iodine and potassiumiodine), thereby forming the Au plated layers 27 and 28.

The effects of the present embodiment will be described. In the presentembodiment, the air gap 10 is formed between the plated feed layer 8/Auplated layer 9 and a portion of the main surface. The air gap 10envelops one end of the drain wiring 5, the gate electrode 4 and thedrain electrode 2 in the device region. Thus, no insulating film of ahigh dielectric constant exists between the semiconductor substrate 1and the gate electrode 4 and between the semiconductor substrate 1 andthe drain electrode 2. Prevention of deterioration of radiofrequencycharacteristics is thus enabled.

Also, in the present embodiment, the device region is completely coveredwith the plated feed layer 25 and the Au plated layer 26. Therefore, nopath exists through which water can permeate into the device region, aslong as separation between the plated feed layer 25 and thesemiconductor substrate 1 in the outer peripheral region at theinterface between the plated feed layer 25 and the semiconductorsubstrate 1 is prevented. Further, the materials of the plated feedlayer 25 and the Au plated layer 26 are metallic materials markedlyresistant to corrosion due to moisture. Covering with the plated feedlayer 25 and the Au plated layer 26 therefore enables improving themoisture resistance, and also enables prevention of damage to the deviceregion and the electrode pads completely covered with the plated feedlayer 25 and the Au plated layer 26 after forming of the plated feedlayer 25 and the Au plated layer 26 in the manufacturing process.

When the semiconductor device according to the present embodiment isimplemented by being packaged, a die bonding surface corresponds to themain surface on which the Au plated layer 26 is provided, and wirebonding is performed on each of the Au plated layers 27 and 28 on thesubstrate back surface.

The present embodiment can be applied to a monolithic microwaveintegrated circuit (MMIC) in which not only active devices such astransistors but also passive devices including a MIM capacitor and amicrostrip line are combined integrally with each other on the mainsurface of the semiconductor substrate 1. In such a case, the platedfeed layer 25 and the Au plated layer 26 completely cover not only thetransistors but also the passive devices. This construction enablesprevention of deterioration (corrosion) of the passive devices even ifthe materials of the passive devices are easy to corrode. Active devicesmay also be formed on the back surface side of the semiconductorsubstrate 1.

Fifth Embodiment

FIG. 23 is a sectional view of a semiconductor device according to afifth embodiment of the present invention. An ohmic metal layer 31 ohmicjoined to the semiconductor substrate 1 is provided in the outerperipheral region of the main surface. The plated feed layer 25 and theAu plated layer 26 are joined to the semiconductor substrate 1 throughthe ohmic metal layer 31. The other components are the same as those inthe fourth embodiment.

When the ohmic metal layer 31 is formed, a eutectic portion is formedbetween the ohmic metal layer 31 and the semiconductor substrate 1 byheat treatment. Therefore, the strength of adhesion in the interfacebetween the ohmic metal layer 31 and the semiconductor substrate 1 ishigher than that in the interface between the plated feed layer 8 andthe semiconductor substrate 1. Therefore, separation between the platedfeed layer 25 and the semiconductor substrate 1, which may lead to theformation of a path through which water can permeate into the air gap10, can be limited to improve the moisture resistance.

Sixth Embodiment

FIG. 24 is a top view of a semiconductor device according to a sixthembodiment of the present invention. FIG. 25 is a sectional view takenalong line I-I in FIG. 24. FIG. 26 is a top view at the heightcorresponding to line II-II in FIG. 25.

The plated feed layer 25 and the Au plated layer 26 are also joined tothe semiconductor substrate 1 in a region between the device region andthe outer peripheral region. This construction enables prevention ofoccurrence of separation between the plated feed layer 25 and the Auplated layer 26 caused, for example, by an external force applied in themanufacturing process even in a case where the strength of adhesionbetween the plated feed layer 25 and the semiconductor substrate 1 islow. The construction in the present embodiment can also be applied tothe fifth embodiment.

Seventh Embodiment

FIG. 27 is a top view of a semiconductor device according to a seventhembodiment of the present invention. FIG. 28 is a bottom view of thesemiconductor device according to the seventh embodiment of the presentinvention. FIG. 29 is a sectional view taken along line I-I in FIG. 27.FIG. 30 is a top view at the height corresponding to line II-II in FIG.29.

Au plated layers 32 and 33 are provided outside the Au plated layer 26on the main surface. The Au plated layer 32 is connected to the Auplated layer 27 through a via hole 34 penetrating the semiconductorsubstrate 1. The connection (not shown) between the Au plated layer 28and the Au plated layer 33 is also made in the same way. The othercomponents are the same as those in the fourth embodiment.

Since external terminals for the gate, source and drain are provided onthe main surface of the semiconductor substrate 1 as described above,the semiconductor device is capable of flip-chip mounting. Therefore,the package can be reduced in size and in thickness. The construction inthe present embodiment can also be applied to the fifth and sixthembodiments.

Eighth Embodiment

FIG. 31 is a top view of internal portions of a semiconductor deviceaccording to an eighth embodiment of the present invention. FIG. 32 is abottom view showing the semiconductor device according to the eighthembodiment of the present invention.

An Au plated layer 35 is provided on the back surface of thesemiconductor substrate 1. The Au plated layer 35 is connected to theplated feed layer 8 and the Au plated layer 9 through a via hole 36penetrating the semiconductor substrate 1. The other components are thesame as those in the fourth embodiment.

Since external terminals for the gate, source and drain are provided onthe back surface of the semiconductor substrate 1 as described above,the semiconductor device is capable of surface mounting. The externalsize of the semiconductor device can be reduced in comparison with theseventh embodiment. Therefore, the package can be further reduced insize and in thickness in comparison with the seventh embodiment. Theconstruction in the present embodiment can also be applied to the fifthand sixth embodiments.

The embodiments have been described with respect to cases where a fieldeffect transistor is provided in the device region on the main surfaceof the semiconductor substrate 1, but a bipolar transistor having a baseelectrode, an emitter electrode and a collector electrode mayalternatively be provided in the device region.

Obviously many modifications and variations of the present invention arepossible in the light of the above teachings. It is therefore to beunderstood that within the scope of the appended claims the inventionmay be practiced otherwise than as specifically described.

The entire disclosure of Japanese Patent Application No. 2011-190751,filed on Sep. 1, 2011, including specification, claims, drawings, andsummary, on which the Convention priority of the present application isbased, is incorporated herein by reference in its entirety.

What is claimed is:
 1. A semiconductor device comprising: asemiconductor substrate having a main surface and a back surfaceopposite each other; first and second electrodes in a device region ofthe semiconductor substrate, on the main surface of the semiconductorsubstrate, and spaced apart from each other; an air gap forming metalfilm on the main surface of the semiconductor substrate and joined tothe second electrode; an air gap between a part of the main surface ofthe semiconductor substrate and the air gap forming metal film,enveloping the first electrode, and having an opening; a cured resinclosing the opening; a liquid repellent film on an internal surfacefacing the air gap and increasing contact angle of the resin, when in aliquid state, relative to contact angles on the semiconductor substrateand the air gap forming metal film; a first metal film joined to the airgap forming metal film, covering the air gap forming metal film and thecured resin, and joined to the semiconductor substrate in an outerperipheral region of the semiconductor substrate, at a periphery of thedevice region of the semiconductor substrate; and a second metal film onthe back surface of the semiconductor substrate and connected to thefirst electrode through a via hole penetrating the semiconductorsubstrate.
 2. The semiconductor device according to claim 1, furthercomprising an ohmic metal layer, ohmically-joined to the semiconductorsubstrate in the outer peripheral region of the main surface of thesemiconductor substrate, wherein the first metal film is joined to thesemiconductor substrate through the ohmic metal layer.
 3. Thesemiconductor device according to claim 1, wherein the first metal filmis joined to the semiconductor substrate in a region between the deviceregion and the outer peripheral region of the semiconductor substrate.4. The semiconductor device according to claim 1, further comprising athird metal film located outside the first metal film, on the mainsurface of the semiconductor substrate, and connected to the secondmetal film through a via hole penetrating the semiconductor substrate.5. The semiconductor device according to claim 1, further comprising athird metal film on the back surface of the semiconductor substrate andconnected to the air gap forming metal film through a via holepenetrating the semiconductor substrate.